The following abbreviations and terms are herewith defined, at least some of which are referred to within the following description of the present disclosure.    3GPP 3rd-Generation Partnership Project    AGCH Access Grant Channel    ASIC Application Specific Integrated Circuit    BLER Block Error Rate    BSS Base Station Subsystem    CC Coverage Class    CCCH Common Control Channel    eDRX Extended Discontinuous Receive Cycle    EC-PCH Extended Coverage Paging Channel    DSP Digital Signal Processor    EDGE Enhanced Data rates for GSM Evolution    EGPRS Enhanced General Packet Radio Service    FN Frame Number    GSM Global System for Mobile Communications    GERAN GSM/EDGE Radio Access Network    GPRS General Packet Radio Service    HARQ Hybrid Automatic Repeat Request    IMSI International Mobile Subscriber Identity    IoT Internet of Things    LTE Long-Term Evolution    MF Multiframe    MFRMS Multiframes    MS Mobile Station    MTC Machine Type Communications    PCH Paging Channel    PDN Packet Data Network    PDTCH Packet Data Traffic Channel    PSM Power Saving Mode    RACH Random Access Channel    RAN Radio Access Network    RAI Routing Area Identity    RAU Routing Area Update    SGSN Serving GPRS Support Node    TDMA Time Division Multiple Access    TSG Technical Specifications Group    UE User Equipment    WCDMA Wideband Code Division Multiple Access    WiMAX Worldwide Interoperability for Microwave Access    Coverage Class: At any point in time a device belongs to a specific uplink/downlink coverage class that corresponds to either the legacy radio interface performance attributes that serve as the reference coverage for legacy cell planning (e.g., a Block Error Rate of 10% after a single radio block transmission on the PDTCH) or a range of degraded radio interface performance attributes compared to the reference coverage (e.g., up to 20 dB lower performance than that of the reference coverage). Coverage class determines the total number of blind transmissions to be used when transmitting/receiving radio blocks. An uplink/downlink coverage class applicable at any point in time can differ between different logical channels. Upon initiating a system access a device determines the uplink/downlink coverage class applicable to the RACH/AGCH based on estimating the number of blind transmissions of a radio block needed by the BSS receiver/device receiver to experience a BLER (block error rate) of approximately 10%. The BSS determines the uplink/downlink coverage class to be used by a device on the device's assigned packet channel resources based on estimating the number of blind transmissions of a radio block needed to satisfy a target BLER and considering the number of HARQ retransmissions (of a radio block) that will, on average, be needed for successful reception of a radio block using that target BLER. Note: a device operating with radio interface performance attributes corresponding to the reference coverage is considered to be in the best coverage class (i.e., coverage class 1) and therefore does not make blind transmissions.    eDRX cycle: eDiscontinuous reception (eDRX) is a process of a wireless device disabling its ability to receive when it does not expect to receive incoming messages and enabling its ability to receive during a period of reachability when it anticipates the possibility of message reception. For eDRX to operate, the network coordinates with the wireless device regarding when instances of reachability are to occur. The wireless device will therefore wake-up and enable message reception only during pre-scheduled periods of reachability. This process reduces the power consumption which extends the battery life of the wireless device and is sometimes called (deep) sleep mode.    Nominal Paging Group: The specific set of EC-PCH blocks a device monitors once per eDRX cycle. The device determines this specific set of EC-PCH blocks using an algorithm that takes into account its IMSI, its eDRX cycle length and its downlink coverage class.
As described in the 3GPP TSG-GERAN Meeting #63 Tdoc GP-140605, entitled “GSM Evolution for cellular IoT—PCH Overview” dated Aug. 25-29, 2014, wireless devices (e.g., those used for machine type communications (MTC)) can operate using different coverage classes and can be expected to make use of different discontinuous receive (DRX) cycles ranging from minutes to hours or even days depending on the frequency of reachability desired for such wireless devices. The entire contents of GP-140605 are hereby incorporated by reference herein for all purposes.
If it is desired that a wireless device supports downlink reachability with a periodicity ranging from about 1 to 30 minutes, then the wireless device should be operated using the extended DRX (eDRX) based reachability, since the Power Saving Mode (PSM) based reachability will not allow for sufficient extension of battery lifetimes (e.g., 10 years) to be realized within this time range. In this regard, the PSM allows the wireless device to save battery life by informing the network about the periodicity with which the wireless device becomes reachable. Since the wireless device in PSM has a limited interval of reachability determined according to when its ready timer is active, delivery of any mobile terminated traffic will be forced to wait until this limited interval of reachability occurs in the wireless device. An increase in the reachability for the wireless device in PSM can be made by increasing the RAU frequency or by increasing the rate at which the wireless device sends periodic keep-alive messages both of which will start the ready-timer in the wireless device thereby making it accessible to the network. However, the increasing of the RAU frequency or the keep-alive transmission frequency are very energy consuming solutions which lower the battery lifetime for the wireless device.
The alternative, or perhaps complement, to the PSM functionality is the eDRX functionality (e.g., as discussed in the 3GPP TSG-GERAN Meeting #64 Tdoc GP-140897, entitled “pCR for uPoD eDRX” dated Nov. 17-21, 2014, the entire contents of which are hereby incorporated herein by reference for all purposes). The eDRX functionality will for a given periodicity of reachability almost always consume less energy than the energy consumed by using PSM. This is due to the energy saved because the wireless device only needs to listen to paging when using the eDRX functionality instead of periodically transmitting a RAU message or keep-alive message as required when using the PSM functionality. FIG. 1 (PRIOR ART) is a graph that illustrates simulated details about the battery lifetime of a wireless device for different triggering intervals when implementing the PSM functionality and the eDRX functionality. The PSM functionality, the eDRX functionality and the simulations comparing the two functionalities are all discussed in more detail in the 3GPP TSG-GERAN Meeting #64 Tdoc GP-140910, entitled “MS Energy Consumption Evaluation, PSM vs. eDRX” dated Nov. 17-21, 2014, the entire contents of which are hereby incorporated herein by reference for all purposes. However, as discussed below, when the eDRX functionality is implemented there can still be problems that should be addressed.
For instance, a SGSN (e.g., core network (CN) node) that has received an IP packet (e.g., containing a trigger) for delivery to a target wireless device that makes use of eDRX will, based on legacy procedures, respond by immediately sending a corresponding paging request for the target device to a BSS (e.g., RAN node). When this occurs, there is the possibility that the next paging based instance of reachability for the target wireless device may occur well beyond the point in time when the BSS receives the paging request. This can be problematic considering that (a) the BSS may be limited in how long the BSS can buffer the paging request while waiting for the next paging opportunity for the target wireless device operating in eDRX mode, and (b) the SGSN may consider the paging request to have failed or the target wireless device to be unreachable if the SGSN does not receive a corresponding page response from the BSS within a relatively short time frame. These problems and other problems are addressed by the present disclosure.